Howard Dean looked close to unstoppable yesterday in his push to become the nation’s new top Democrat, as two more rivals dropped out to boost him and a key union leader backed his bid to be Democratic National Committee chair.

Former Rep. Martin Frost (Texas), a one-time rival who dropped out, congratulated Dean as the likely winner, and Ohio chair David Leland quit the race and backed Dean for the Feb. 12 vote. So did American Federation of Teachers chief Edward McElroy.

Frost had hoped for AFL-CIO support in a stop-Dean bid, but the AFL declined to make a unified endorsement.

Dean aides now claim 103 votes of the 214 needed to become DNC chief and control a budget that totaled $400 million last year, but DNC insiders say he’s over 120. His chief rival, Donnie Fowler, claims about 50.